The electric power transmission networks of ships are relatively small. Generators are connected thereto for supplying the ship's demand of electric power. Each generator is driven by a power source, such as a diesel engine. The generators run in the electric network at the same speed so as to have the same frequency in all places of the electric network. It is not possible to economically store electricity, so the production of electricity must correspond to the consumption of electricity of the network. Thus there must be some kind of arrangement in the power transmission network for distributing the load among the generators.
A known way is to use droop adjustment, i.e. deviation adjustment. Each generator has a power production line as a function of the frequency of the network. When the load is large, the frequency of the network tends to increase, and when the load is small, the frequency tends to increase. Thus, the disadvantage is that the frequency of the constant state of the system depends on the load of the system.
Another way is to use so-called isosynchronic load distribution. In this method the average load of the system is used for establishing the set values for the generators for distributing the load. The principle of the isosynchronic adjustment is similar to deviation adjustment, but it does not depend so much on the load of the network.
Digital data communication buses have become more common to replace the older analog buses used for load distribution. The advantages of digital buses are their accuracy, reliability, lack of disturbances. Analog solutions have, however, been very adaptable to various configurations of the network. With a digital solution, it is difficult to mimic an analog power transmission network. Typically the power transmission network comprises switches the state of which can be changed, if necessary, either automatically or manually. Software, circuit board or other apparatus used for load distribution easily becomes very complex.